Dear Editor,A 41-year-old woman presented with an approximately one-year history of progressive
facial swelling and left-sided visual impairment. A computed tomography (CT) scan of the
skull showed a sclerotic, expansile lesion on the lateral/upper wall of the left orbit,
narrowing and extending to the optic canal. Magnetic resonance imaging (MRI) showed a
lesion with a hypointense signal in T1-weighted and T2-weighted sequences, without
significant contrast uptake, accompanied by a slight contrast-enhanced thickening of the
subjacent dura mater, which was compressing the left optic nerve. A histopathological
study confirmed the suspected diagnosis of intraosseous meningioma.Recent studies in the radiology literature of Brazil have emphasized the importance of
imaging examinations in improving the diagnosis of central nervous system
disorders([1]-[3]). Meningioma is the most common primary intracranial
tumor, representing approximately 14-20% of cases. The vast majority are intradural
lesions, extradural lesions accounting for only 1-2%([4]). Extradural meningiomas
affect the cranial vault in 68% of cases, such lesions being referred to as primary
intraosseous meningiomas (PIMs), which mainly affect the frontal and parietal bones, as
well as the region of the orbit([5]-[7]). Other common locations for extradural involvement are
the subcutaneous tissue, paranasal sinuses, and parapharyngeal spaces, as well as, in
rare cases, the lungs and adrenal glands([5],[6]). Unlike typical intradural meningiomas, which primarily
affect females between the ages of 50 and 69 years and usually have a benign course,
PIMs can affect either gender, have a peak incidence in the second decade of life, and
are more likely to evolve to malignant degeneration([6]).A: Axial CT scan, with bone window settings, showing an
expansile, osteoblastic lesion, affecting the upper/lateral wall of the left
orbit (arrow). B: Noncontrast sagittal T1-weighted MRI
sequence, showing a lesion with a hypointense signal (arrow).
C: Coronal T2-weighted MRI sequence, also showing the
lesion with a hypointense signal (arrow). Also note the compressive effect
and displacement of the intraorbital structures, including the optic nerve.
D: Contrastenhanced coronal T1-weighted MRI sequence,
showing a lack of significant contrast uptake within the lesion (arrowhead),
with only slight uptake in the dura mater subjacent to the tumor
(arrow).On CT, most PIMs (65%) present as expansile, osteoblastic bone lesions, with or without
cortical destruction([6]). On MRI, they commonly hypointense in T1- and
T2-weighted sequences, typically without significant contrast enhancement, as in the
case reported here([5]). However, in rarer cases, if a PIM presents as an
osteolytic lesion on CT, an MRI scan can show a hypointense signal in T1-weighted
sequences and a hyperintense signal in T2-weighted sequences, as well as contrast
enhancement([6],[7]). Although PIMs do not present the dural tail sign that
is often found in intradural meningiomas, there can be contrast uptake in the dura mater
subjacent to the tumor due to venous stasis or to tumor invasion, as demonstrated in our
case([7]).
There are inherent differences between CT and MRI, the former allowing better
delineation of bone involvement, whereas the latter provides a better assessment of the
soft-tissue involvement and extradural extent of the lesion([6]).The differential diagnosis of osteoblastic PIM includes typical intradural meningioma
with reactive hyperostosis, in which the meningeal component of the lesion is the most
obvious. Other diagnoses that should be considered are metastases, plasmacytoma, fibrous
dysplasia, osteoma, osteosarcoma, and Paget’s disease([6]).In most cases of PIM, the treatment is total surgical resection, with subsequent cranial
reconstruction. If the resection is partial, there should be radiological follow-up; if
the disease has recurred or if the residual lesion has progressed, the next surgical
procedure can be accompanied by adjuvant radiotherapy([6]).In conclusion, although rare, PIMs should be considered in the differential diagnosis of
bone lesions, especially when the lesions are osteoblastic and located in the cranial
vault.